1. Field of the Invention
The present invention relates to a three-dimensional image display apparatus which synchronizes with a rotation angle of a rotating two-dimensional display device so as to display a three-dimensional image by switching and displaying an image on the two-dimensional display device.
2. Description of the Related Art
It is desired that a three-dimensional image display apparatus for displaying a three-dimensional image (which may be referred to as a three-dimensional display unit) should be realized in a lot of application fields, such as a medical filed, a chemical field (molecule structural analysis), a machine design filed (CAD), an advertising display filed, and an entertainment field.
Consequently, as a three-dimensional display unit, a system using binocular parallax is put into practical use. For example, a 50-inch type three-dimensional display unit having four viewpoints is presented, and a mobile telephone incorporating a three-dimensional display function is put into practical use.
Although it is possible for these three-dimensional display units which use the binocular parallax to display a three-dimensional image comparatively easily by means of a flat display unit, a viewpoint position allowing stereoscopic vision is limited, so that a viewer cannot observe an image from an arbitrary position.
As the result, a system with which the viewer can observe a three-dimensional image from an arbitrary position, a volumetric scan type three-dimensional display unit is known and put into practical use as a product.
FIG. 32 is a view showing a schematic structure of this volumetric scan type three-dimensional display unit. A three-dimensional display unit 132 comprises a base unit 134, a screen 136 rotating at a high speed revolution (730 rpm) on the base unit 134, and a windshield 138 for housing the screen 136. The base unit 134 has therein an optical system constituting a projector which projects an image on the rotating screen 136 by means of a DMD (Digital Micro-mirror Device), and its projection mirror section 140 is provided on an upper surface of the base unit 134. By synchronizing with a rotation angle of the screen 136, this projection function performs switching and projecting a cross-sectional image of a three-dimensional object on the screen 136.
Now, a principle which performs display of the three-dimensional image by means of the above-mentioned volumetric scan type three-dimensional display unit will be described by using FIG. 15. It is assumed that a certain spherical three-dimensional object 142 is displayed as shown in FIG. 33A. It is further assumed that a surface cutting image, namely, a surface sectional image of this three-dimensional object 142 is considered in the situation where the screen 136 is rotating continuously and the screen 136 is at a certain rotation angle.
As shown in FIG. 33B, at the time of an angle (rotation angle) of 1, the screen 136 is in the position where the screen 136 slightly enters the three-dimensional object 142, whose surface cutting image (hereinafter referred to as a cross-sectional image) is a small circle 144 in the beginning as shown at an angle of 1 in FIG. 33C. Similar to the above description, as the screen 136 enters the three-dimensional object 142, a size of the cross-sectional image changes. The size of the circle 144 is the maximum at an angle of 3. Then, at an angle of 5, it becomes smaller. Finally, the screen 136 disengages from the three-dimensional object 142.
In this way, for each angle of the screen 136, a cross-sectional image of the three-dimensional object as shown in FIG. 33C is projected and displayed on the screen 136 through the projection mirror section 140. When the screen 136 is rotating at a high revolution speed at this time, an integral effect in an eye causes the screen 136 to be invisible and all the displayed cross-sectional images to be visible as a residual image, so that a three-dimensional image of the three-dimensional object 142 is displayed as a set of the continuous cross-sectional images. In order to obtain this effect effectively, a volume rewriting cycle is desirably 30 Hz or more (although there are some flickers at a lower cycle, it is possible to display a three-dimensional image). Therefore, the number of revolutions of the screen 136 is desirably 15 Hz (900 rpm) or more.
However, in order to display an image on the rotating screen 136 by using a projector, it is necessary to reflect a video image on the mirrors by a plurality of times. Therefore, in order to display the image with sufficient accuracy, it is necessary to precisely establish a complicated reflective system by means of the mirrors, this increases a cost of the device. First of all, it is difficult to improve a display accuracy, thus only a fuzzy three-dimensional image is obtained. Moreover, there is a problem that it is also difficult to get higher brightness and contrast of the three-dimensional image.
A method of solving the problem of such a three-dimensional display unit may be a system in which an image is switched and directly displayed on the rotating self-luminous two-dimensional display device (the same as the two-dimensional display panel) while synchronizing with the rotation angle thereof, without using a projector. This system performs clearly displaying of a three-dimensional image, and improving the display accuracy, the brightness and the contrast. A basic idea of such a system is known (for example, see Patent Document 1).
Patent Document 1: International Publication No. S56-500313 (Japanese Translation of PCT International Application)